Many chemical heaters have been proposed in the past. Hill et al. (2001) provides one overview of potential reactions. The object of this invention is to teach a device that not only generates temperatures in excess of about 150° F. over about 15 minutes or less, but also provides the means to filter microbes from non-potable water using the same exothermic reaction.
U.S. Pat. No. 3,079,911 (Ryan et al., 1963) describes a heating device that generates heat by the oxidation of a metal, activated by the addition of water. The reactants are a mixture of aluminum, copper sulfate, potassium chlorate, and calcium sulfate, which generates flammable or corrosive gases. U.S. Pat. No. 4,559,921 (Benmussa, 1985) shows a self-heating device using a sealed container holding calcium oxide and water. The calcium oxide and water are kept separate by a sealed pouch. A tearing element affixed to the pouch opens the pouch and the container, allowing water to contact the calcium oxide, starting the exothermic reaction to heat the food. Similarly, U.S. Pat. No. 4,809,673 (Charvin, 1989) describes the hydration of calcium oxide to generate heat. The heat output per weight (of the dry material) is approximately 501 Btu/lb and inferior to other reactions. U.S. Pat. No. 5,205,277 (Chao-Tsung, 1993) also describes a self-heating container using three heating packs based on a calcium oxide reaction. U.S. Pat. No. 4,753,085 (Labrousse, 1988) describes reactions using sodium hydroxide with hydrochloric acid. Although this reaction produces more heat per weight of heater material (565 Btu/lb) than the hydration of calcium oxide discussed above, it requires the handling of a strong acid, HCl. The inventors also describe the oxidation of iron powder to produce heat, but this reaction is muted by water. As will be discussed later in this section, these reactions have a heat of reaction about an order of magnitude less than the nameless ration heater (FRH) reaction at 6267 Btu/lb. The FRH reaction (Mg reacted with water and catalyzed by Fe), was originally developed by the U.S. Army Meals-Ready-to-Eat (MRE's).
In U.S. Pat. No. 4,751,119 (Yukawa, 1988), a liquid and solid reactant are combined to produce heat. The reactants include quicklime (CaO), sodium hydroxide, cobalt, chromium, iron, iron hydroxide, magnesium, manganese, magnesium chloride, molybdenum, tin oxide (II), titanium, sodium, calcium hydroxide, sulfuric acid, nitric acid, and metallic sodium. The reactants generate an oxide reacting with oxygen at room temperature in the form of a metal or a metallic compound and have an exothermic characteristic. The reaction has a heat output per weight of reactant of only 721 Btu/lb requiring large masses of material. This again is about one order of magnitude less than the FRH reaction.
In another chemical heater, U.S. Pat. No. 4,819,612 (Okamoto et al., 1989) describes a container capable of heating beverages or soups when ignited (by a match, for instance). This heater functions by oxidation or combustion using potassium permanganate, manganese dioxide, trilead tetraoxide, barium peroxide, bromates, and chlorates with the combustible compounds including metal powders of iron, silicon, ferrosilicon, aluminum, magnesium, and copper. The reaction is not activated by water but by an initiator such as a spark lighter. The reaction temperature can exceed 1000° C., which creates many packaging problems. U.S. Pat. No. 4,949,702 (Suzuki et al., 1990) also describes a self-heating device including a heater within a container that does not use water. The heater includes a pyrogen of high heating value and an initiator that is ignited by spark. Both elements are metal oxides or metals. This reaction may also require a power source, which is undesirable for a food heater/hydrator.
Bell et al. (2001) also propose a two-component solid reaction that is initiated by water. This reaction uses combinations of CaO, AlCl3, and P2O5. Reactions involving CaO and AlCl3 consume water, whereas reactions with CaO and P2O5 require water as a reactant but regenerate it so there is a net use of oxygen. The heat of reaction for these combinations is also inferior to the FRH reaction.
The present inventors also developed a “Self-Contained Atmospheric Protective Ensemble” (SCAPE) suit heating system for NASA (Scaringe et al., 1992). This project included an exhaustive study of potential chemical heating candidates, including electrolyte/water (solid/water, liquid/water, gas/water) and phase change materials. Any electrolyte/water system that was toxic, corrosive, or carcinogenic was not considered. Sodium oxide (Na2O) was found to be a viable reaction candidate for energy generation. This project also developed an automatic water control valve using a bimetallic creep-disk valve that administered water over a 2-hour period for heating. A wicking component was also developed to transport water through the Na2O bed to prevent caking. Although this reaction is rapid and produces high temperatures, its heat of reaction is still inferior to the FRH reaction.
U.S. Pat. Nos. 5,117,809 (Scaringe et al., 1992) and 5,390,659 (Scaringe et al., 1995) describe a heater material utilizing the same alloy of magnesium and iron as described in U.S. Pat. No. 4,522,190 (Kuhn et al., 1985) but with a different packaging arrangement. U.S. Pat. No. 5,117,809 (Scaringe et al., 1992) also describes the use of other known exothermic reaction materials, including calcium oxide, anhydrous calcium chloride, magnesium oxide, zeolite molecular sieves, and silica gel. All of these react with water to give off heat; however, the Mg—Fe system produces the best exothermic heats of reaction.
The current FRHs make use of a reaction between Mg and water catalyzed by Fe. The Army has also performed considerable R&D on this reaction (see Pickard et al., 1993-1994). This reaction is initiated by water with a heat of reaction equal to 6,267 Btu/lb Mg. Portable heaters that function well in the presence of water are more desirable because water serves both to transfer heat from the heater to the food or other object to be heated, particularly by evaporation/condensation, and to limit the temperature of the heater by removing the heat of vaporization once the boiling point of water is reached. U.S. Pat. No. 4,522,190 (Kuhn et al., 1985) describes a heater material for heating food and other items, which came to be known as the FRH. The heater is a composite of “supercorroding” metallic alloy powder distributed throughout a porous ultra-high-molecular-weight (UHMW) polyethylene. The supercorroding metallic alloy is preferably a powdered combination of magnesium and iron, which when wetted with an electrolytic solution such as aqueous sodium chloride produces heat.
The heat of reaction for Corrodalloy-5 (FRH chemical composition commercially available through Dymatron) with water produces large exothermic heats. We concluded from a study of the literature, as well as screening experiments, that this reaction is the preferred basis for heating and hydrating food and beverages. Numerous reactions were evaluated involving the chemicals P2O5, CaO, Na2O, AlCl3, and KO2, to name a few, but the FRH reaction was superior in exothermic heat of reaction, providing a foundation for this invention. The FRH reaction also has advantages in that it produces a gas product for pressurization and is familiar to the Army as a component in MRE's. The FRH reaction unmodified was not directly suitable for a heating and hydrating system, so improvements and modifications to the formulation were needed and are the subject of this invention.
The second component of the heater and hydrating device is the purification of water from a source such as a lake. Several processes can be used to purify water for use in food or beverage rations, including ion exchange, distillation, and membrane filtration. Ion exchange is not feasible because large quantities of material are needed. Distillation is undesirable because it requires power. Membrane filtration is really the only viable option.
Hydration Technologies, Inc. (HTI) has developed a pouch design (“X-Pack”) for forward osmosis (www.hydrationtech.com). This design uses forward osmosis, driven by an electrolyte on the downstream side of a reverse osmosis (RO) membrane. The filtration time for this membrane system is also quite lengthy, requiring up to 6-12 hours for 12 fl oz of water. Higher temperatures may increase this flux rate to less than 30 minutes. To overcome the osmotic pressure upstream of the membrane, pressures of 400 and 20 psid must be supplied for saltwater and brackish water feed, respectively.
Using an electrolyte solution downstream of the membrane to drive the process will not be feasible for many foods or beverages because it would impart an undesirable taste. Therefore, the only alternative is to use membrane filtration in the reverse mode. In order to use membrane filtration in the reverse mode, pressure must be supplied to the upstream side of the membrane to overcome osmotic pressure. For the heating and hydration process to proceed, a passive chemical reaction must therefore be provided that generates heat and pressure.
Chemical biocide formulations have also been taught in U.S. Pat. Nos. 5,632,904, 6,303,039, and 6,638,431 by the present inventors. Formulations such as these can be integrated into self-heating and self-hydrating devices such as that taught in this invention, to provide additional water disinfection if needed.
Recognizing the deficiencies in past chemical heater reactions, namely, high temps, explosiveness, low or no pressure generation, and toxic or corrosive materials, we discovered an improved chemical formulation based on the FRH reaction with improved and advantageous properties required for a water heating and hydrating device. We also contemplate that other reactions which are exothermic and pressure generating, can be used to heat and hydrate foods from non-potable water.